In digital signal processing, sampling/frame rate conversion has various applications. In the multimedia compression, transformation, networking and display markets, it is often the case that an audio sample at one rate needs to be converted into a second, or target rate that is different. For example, professional audio equipment may utilize a higher audio processing rate than consumer electronics, which operate at a lower processing or sampling rate. To save storage, processing and transmission bandwidth resources, the rate conversion is usually a “downward” conversion. Specifically, the encoding rate is reduced. There are some transcoding processes or synchronization re-alignments in audio and video applications (both storage and transmission) that require resampling and time-mapping processing.
Due to the discrete mode of the human vision model, humans can tolerate some image dropping or insertion during a video sequence to a significant extent. However, the human ear can detect even small audio data distortions or losses, and these can rapidly become annoying to the listener. Thus, merely dropping bits from the sample is not desirable to effect the conversion.
In general, the frame/sample rate conversion and related time stamp conversion designs are application specific and have variations in terms of quality, complexity, feature, resource usage and other attributes.
The polyphase filter with a finite impulse response (“FIR”) structure is a very popular and effective approach for the sampling/frame rate conversion tasks. However, a polyphase FIR filter's implementation can become difficult, cumbersome or unfeasible on some platforms, in terms of efficiency, precision, robustness, and resource usage, when the sampling rate conversion becomes complex and interpolation and decimation factors are high.
Some resampling applications demand a wide range of flexibility and must adapt to the real-time resampling variation or even unknown resampling ratio. Therefore, there is a need for a flexible architecture to perform sampling/frame rate conversions for audio applications in a lower cost, and more effective manner.